Bioassay Directed Chemical Study Of Antimalarial Substances From Clerodendrum Myricoides And Dodonaea Angustifolia And Comparative Chemical Studies Of Moringa Stenopetala And Moringa Oleifera

Human beings have since time immemorial used plants for different purposes including as food,rnfor flavor, cosmetic, dying clothes, and above all as medicine for treating a wide spectrum ofrndiseases. The main aim of this dissertation work is to find rationale for the use of selected plants inrncombating one of the most challenging diseases in the world, namely, malaria. The selection of thernplant materials for the study was based on ethnomedicinal uses. This led to the need for systematicrninvestigation of two plants, Clerodendrum myricoides (Lamiaceae) and Dodonaea angustifoliarn(Sapindaceae), which are indigenous medicinal plants traditionally used as remedies againstrnmalaria in some parts of Ethiopia. In the course of this study, bioassay guided investigation on thernantiplasmodial activities of the leaves of C. myricoides resulted in the isolation of two activerncompounds, namely, α-spinasterol (63) and sitosterol-3-O-β-D-glucoside (64), which significantlyrnsuppress parasitaemia by 51% and 44% at 40 mg/kg, respectively.rnFurthermore, the acetone extract of the leaves of C. myricoides afforded verbascoside (12),rnixoroside (73), and compound 71. To our knowledge there is no report in the literature forrncompound 71. Tetracosanoic, behenic, icosanoic, stearic, and palmitic acid were also identifiedrnfrom the leaves of this plant. Investigation of the radical scavenging activities of the abovernconstituents resulted in verbascoside as the most active compound comparable to ascorbic acid. Bioassay guided fractionation of the ethyl acetate soluble portion of the 80% aqueous MeOHrnextract of the leaves of D. angustifolia afforded three compounds, namely, pinocembrin (86),rnsantin (81) and 15,16-epoxy-2-hydroxy-3,13(16),14-clerodtriene-18-oic acid (128) whichrnexhibited high percent suppression of parasitaemia by 81% at 40 mg/kg, 80% at 50 mg/kg andrn70% at 40 mg/kg, respectively. Under similar conditions chloroquine suppressed parasitaemia byrn100% at 25 mg/kg. Column chromatographic fractionation of the ethyl acetate soluble portion ofrnthe ethanol extract of D. angustifolia leaves gave three other compounds in addition to 81, 86 andrn128, identified as 5,7,4’-trihydroxy-3,6-dimethoxyflavone (80), ent-16-hydroxy-labdan-3α,8β-rndihydroxy,13(14)-en-15,16-olide (114), and 5,6,7-trihydroxy-3,4’-dimethoxyflavone (125). Tornour knowledge compound 125 has not been reported before as a natural product. The extracts andrnthe four flavonoids isolated from the leaves of D. angustifolia were tested for their antiradicalrnproperties, which led to 5,7,4’-trihydroxy-3,6-dimethoxyflavone (80) as the most active compound.rnThe leaves of two Moringa species, M. stenopetala which is confined to the horn of Africa namelyrnEthiopia, Somalia and Kenya and M. oleifera originally from the Indian subcontinent but nowrncultivated in different parts of the world including Africa, were compared with respect to theirrnmain chemical constituents. Different techniques including TLC, HPLC-MS, and UV-Visrnspectrophotometry were employed. Our results unambiguously showed significant differences inrnthe chemical profiles of the leaves of the two species. Rutin (163) is the only principal flavonoidrnglycoside of the leaves of M. stenopetala, which however is not detected in the leaves of M.rnoleifera. On the other hand M. oleifera contains significant amounts of two other glycosides,rnnamely, quercetin-3-O-β-D-glucoside (159) and kaempferol-3-O-β-D-glucoside (161). Thesernresults are significant in distinguishing the two Moringa species. Furthermore, a simple highrnperformance thin layer chromatographic method was developed and validated for quantitativernanalysis of rutin in the leaves of M. stenopetala. The level of rutin in the leaves of M. stenopetalarnwas found to be 1.9±0.08%. These fingerprinting results can be used not only to differentiate therntwo species but also to establish presence or absence of adulterants, an issue that is significant inrnthe use and marketing of crude and derived products from Moringa leaves Further chemical investigation on the leaves of M. stenopetala afforded three compoundsrnidentified as heptacosanol (185), sitosterol-3-O-β-D-glucoside (64), and inositol dimer (186). Thernseed kernel and husk of M. stenopetala was also investigated in this study for the first time. Thisrnresulted in the isolation and characterization of stearic acid (77), 4-(α-L-rhamnopyranosyloxy)rnbenzyl glucosinolate (164) and sucrose (187) from the seed kernel while the husk furnishedrnallantoin (191) and compound 190. To our knowledge compound 190 was not reported before asrnnatural product. GC-MS analysis of the fatty acids of the oil of M. stenopetala afforded oleic acidrn(52%), stearic acid (9%), palmitic acid (9%), behenic acid (5%), archidic acid (5%), palmitoleicrnacid (1%) and myristic acid (0.2%). The above flavonoid glycosides displayed pronounced radicalrnscavenging and anti-lipid peroxidation activities.rnKey words: Bioassay, Clerodendrum myricoides, Dodonaea angustifolia, Sapindaceae, Lamiaceae,rnAntiplasmodial, radical scavenging, pinocembrin, santin, verbascoside, Moringaceae, Fingerprint,rnHPLC-MS, TLC, UV, Moringa stenopetala, Moringa oleifera, quality control, radical scavenging

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